Next-generation mobile communication systems to be used mainly for video and data communications require capability far greater than that of the third generation mobile communication system (IMT-2000) to achieve high-volume, high-speed broadband communications. In such a next generation system, packet switching is used, instead of conventional circuit switching, even for wireless sections to improve the use efficiency of communication resources. Meanwhile, there are various indoor and outdoor communication environments. In the outdoor communication environment, for example, multiple cells (multi-cell) covering a broad area are set up to enable high-speed packet transmission for mobile stations moving at high speed. In the indoor communication environment where attenuation of radio waves is high, indoor access points are used instead of outdoor base stations to support wireless communications. Also, for communications between base stations or upper devices and mobile stations, especially for downlink data transmission, multicast and broadcast are used in addition to unicast (for future trends of communication systems, see, for example, non-patent document 1).
In a broadband mobile communication system, the influence of frequency selective fading due to the multipath environment is significant. To solve this problem, orthogonal frequency division multiplexing (OFDM) is expected to be used for next-generation communication systems. In OFDM, a symbol comprises an effective symbol section containing information to be transmitted and a guard interval attached to the effective symbol section, and multiple symbols are transmitted during a transmission time interval (TTI). The guard interval is generated based on a part of information in the effective symbol section. The guard interval is also called a cyclic prefix (CP) or overhead.    [Non-patent document 1] Ohtsu: “A Challenge to Systems beyond IMT-2000—Approach from Wireless—”, ITU Journal, Vol. 33, No. 3, pp. 26-30, March 2003